1. Field of the Invention
The present invention relates generally to the electrodeposition of metal, and more particularly, to an electrowinning cell and an electrolyte flow system therefor. While the present invention is particularly applicable to an electrowinning process for forming copper, and will be described with reference thereto, the invention also finds advantageous application in electrodepositing other types of metals and metal compounds.
2. Description of the Related Art
It is well known that metal can be extracted from metal ions in an electrolytic solution through an electrowinning process. An electrowinning process utilizes the known technique of plating metal or metal compounds out of an electrolytic solution onto an electrode plate. Modern electrowinning typically occurs in a relatively large, non-conductive tank that contains metal ions dissolved in an electrolytic solution. A plurality of side-by-side, parallel cathode and anode plates are suspended in the electrolytic solution. In a copper electrowinning cell, the cathodes and the anodes are ultimately arranged such that each cathode is disposed between two anodes. The cathodes and anodes are connected to an electrical power source to cause the plating of copper onto the cathode plates.
Electrowinning cells typically include a circulating system that circulates the electrolytic solution from a reservoir to the electrowinning cell and back to the reservoir. Metal ions depleted from the electrolytic solution during the electrodeposition process, are replenished in the reservoir. The replenished (i.e., xe2x80x9cfreshxe2x80x9d) electrolytic solution is pumped into the electrowinning tank, typically at the bottom thereof. Excess solution in the tank overflows the upper edge of the tank and is collected in a trough. The collected (i.e., xe2x80x9cmetal depletedxe2x80x9d) electrolyte is returned to the reservoir.
This type of arrangement produces a less than desirable flow of the electrolytic solution in the tank. The electrolytic solution typically flows from its point of entry at the bottom of the tank toward the edge of the tank where the solution exits, i.e., overflows, the tank. This produces areas of lower flow between the plates, that is more marked in the middle of the upper region of the tank. The flow of the electrolytic solution is also influenced by gas bubbles that form between the electrode plates during the electrodeposition process, as gas is liberated at the surface of the anode plates. These gas bubbles also tend to direct the electrolytic solution away from the spaces or gaps between the parallel anode and cathode plates toward the sides and edges of the tank. Thus, the replenished, fresh electrolytic solution forced into the tank typically flows toward the edges of the tank where it overflows the tank, rather than into the cathode and anode gaps where the actual electrodeposition occurs and where the replenished electrolytic solution is needed.
The present invention overcomes these and other problems and provides an electrowinning cell and a circulation system therefor, wherein fresh electrolytic solution entering the tank is directed more uniformly between the cathode and the anode plates.
In accordance with the present invention, there is provided an electrowinning cell that is comprised of a tank for holding electrolyte. The tank has an opened upper end. A plurality of flat, metallic electrode plates are disposed within the tank in side-by-side, spaced-apart, parallel relationship, the electrode plates defining a gap between adjacent electrode plates. An electrolyte circulation system includes an inlet manifold disposed below the electrode plates, and a plurality of spaced-apart collectors extending across the open upper end of the tank. The collectors extend parallel to the electrode plates. Electrolyte is continuously pumped into the tank through the inlet manifold. The electrolyte pumped into the tank flows upward through the gaps to the collectors, the collectors establishing a level for the electrolyte in the tank.
In accordance with another aspect of the present invention, there is provided an electrowinning cell, having a tank, electrolyte within the tank and a plurality of flat, metallic electrode plates disposed within the tank in side-by-side, spaced-apart, parallel relationship. Adjacent electrode plates define an electrode gap therebetween. An electrolyte feed line is provided for injecting electrolyte into the tank below the lower portions of the electrode plates. An electrolyte collector grid comprised of a plurality of generally parallel collectors that extend across the tank are disposed between the electrode plates and establish a level of electrolyte in the tank by collecting the electrolyte when the electrolyte reaches the level. The collectors are disposed relative to the inlet feed line to collect the electrolyte solution at spaced-apart locations within the tank and -to produce a generally vertical flow of electrolyte through the gaps between the electrode plates.
In accordance with another aspect of the present invention, there is provided an electrowinning cell, having a tank having an opened upper end defined by a tank edge, electrolyte within the tank and a plurality of flat, metallic electrode plates disposed within the tank in side-by-side, spaced-apart, parallel relationship. Adjacent electrode plates define an electrode gap therebetween. An injector manifold is disposed at the bottom of the tank for feeding electrolyte into the tank at locations below the electrode plates. An electrolyte collector grid comprised of a plurality of collector ports defines an upper level of the electrolyte by collecting the electrolyte from the tank. The ports are disposed in spaced-apart relationship across the open upper end of the tank. The collector grid and the injector create a flow of the electrolyte upward between the plates as the solution flows from the manifold locations below the plates to the collector ports.
In accordance with another aspect of the present invention, there is provided a method of electrowinning copper, comprising the steps of:
(a) vertically orienting a cathode plate between two, spaced-apart, vertical anode plates within a tank, the cathode plate and the anode plates being essentially parallel to each other with a uniform gap defined between the cathode plate and each anode plate;
(b) negatively energizing the cathode plate and positively energizing the anode plates; and
(c) causing a vertical, upward flow of electrolyte through the gaps between the cathode plate and the anode plates 1) by forcing electrolyte into the tank below the cathode and anode plates and 2) by collecting the electrolyte with a plurality of collector ports disposed across the tank between the anode plates.
In accordance with another aspect of the present invention, there is provided a method of electrowinning copper as described above, further comprising the step of:
(d) causing the electrolyte to flow through the gaps between the cathode plate and the anode plates at a uniform, average velocity of between 0.50 in./min. and 10.0 in./min.
It is an object of the present invention to provide an electrowinning cell having improved operating characteristics.
It is another object of the present invention to provide an electrowinning cell as described above for electrowinning copper.
Another object of the present invention is to provide an electrowinning cell as described above having improved electrolyte flow between the electrode plates.
It is an object of the present invention to provide an electrolyte circulation system for an electrodeposition cell.
It is another object of the present invention to provide an electrolyte circulation system as described above that produces uniform flow of electrolyte past electrode plates in an electrowinning cell.
A still further object of the present invention is to provide an electrowinning cell and electrolyte circulation system as described above that improves the product quality and productivity of the electrowinning cell.
These and other objects and advantages will become apparent from the following description of a preferred embodiment of the invention taken with the accompanying drawings and the appended claims.